Many devices are employed in industry to sense force exerted by the weight of material within a storage bin, tank or other container and to produce an output signal proportional to the force. The output signal may then be employed, through gauges or other readouts, to indicate the level, weight, or volume of material in the container. Alternatively, the output signal may be used to control the flow of material to or from the container via valves, pumps, or other means well known in the art so as to maintain a relatively constant material level, weight or volume in the container.
A significant drawback to most prior art sensing devices and control systems employed therewith is their dependence upon a relatively constant, non-fluctuating source of electrical power. In addition, electrical components and circuits are susceptible to damage and destruction from vibration, shock forces, corrosion, and temperature extremes. Such devices also require regular testing and maintenance to ensure their proper operation. Moreover, even if the sensing devices continue to operate under adverse vibration and temperature conditions, or in otherwise hostile environments, the accuracy of the generated output signal may deteriorate significantly. Finally, the use of electrically powered sensing devices and control systems is highly dangerous in the presence of flammable gases and other materials which may be ignited by electrical sparks.
While a few non-electrical load sensors using hydraulic principles are on the market, such devices are complex and relatively expensive to produce and to maintain in good working order, particularly in hostile environments. Moreover, these devices require ancillary equipment such as pressure boosters to maintain hydraulic pressure for operation. In addition, use of these prior art load sensors as control mechanisms requires the addition of a transducer to convert the hydraulic sensor signal to a pneumatic signal, as the hydraulic sensor generates a high pressure, low volume displacement signal which is unsuitable to control a valve or other mechanism without such conversion.
A major failing of the prior art has been the inability to provide an accurate, relatively trouble-free sensing device and control system which can survive in hostile environments for protracted periods of time without constant attention and maintenance. There has been a particular long-felt need for such a device in field operations of the oil and gas industry, many of which are conducted in remote areas of the world without reliable electrical power and/or on exploration and production platforms miles offshore in areas of predominantly bad weather. The use of electrically powered devices at offshore well sites in particular presents a danger so great that many well operators have instituted extremely strict design requirements which add greatly to the cost of systems employing such devices. As noted previously, while hydraulic load sensors are known in the art, they are complex, precision-manufactured devices requiring a high level of care and attention. Moreover, such sensors are not suitable as control devices without the use of additional equipment.
An additional problem with prior art load sensors has been the inability to target a specific load range and generate an accurate signal when the minimum load on the sensor is substantial.